Most conventional fire doors are provided with vision panels, which are typically sold as a separate assembly. The vision panel assemblies usually include a metal frame and a transparent fire-resistant wire glass panel, which is clamped by the frame in the manner of my U.S. Pat. No. 4,550,542.
The vision panel frames for certain commercial vision panel assemblies must be constructed of steel to withstand a 1700 degree Fahrenheit fire test, while the fire door has a wood veneer exterior and an insulating mineral core interior. The nut and bolt assemblies used to clamp the metal vision panel frames to the fire door are exposed in certain commercial vision panel assemblies.